PROJECT ABSTRACT About one in three children in the U.S. enter kindergarten unprepared to learn and lacking sufficient communication skills. Despite the federal mandate for early intervention (EI), less than 25% of children who will require special education at school age are receiving EI services. A confluence of empirical research on poverty, environmental risk factors, and brain development shows that early experiences are uniquely powerful in the first years of life, providing further impetus for early detection and intervention. Measures of early- developing social communication skills offer a viable solution for earlier detection of children with language delays and subsequent educational challenges. We propose testing a new technology-supported platform with three parent-mediated intervention components for babies with early communication delays using mobile technology: 1) the Social Communication Growth Charts, a self-guided app to explore video clips illustrating early milestones and to chart their child?s development; 2) Baby Navigator Class, group weekly online meetings designed as a companion to the Growth Charts; and 3) Mobile Coaching, individual weekly telehealth sessions to coach parents in their everyday activities. In response to PA-18-145, we propose using a multiphase optimization strategy (MOST) as a framework for development, optimization, and evaluation of our dynamic web intervention platform and prepare for a full-scale 2-stage sequential multiple assignment randomized trial (SMART) design. We will recruit 80 children with communication delays at 12 months of age. Families will be invited to the Social Communication Growth Charts bundled with the Baby Navigator Class. At 18 months, slow responders will be randomized to continue the bundle with or without Mobile Coaching, and responders will continue the bundle. Child outcome measures include social communication, internalizing and externalizing behaviors, and vocabulary at 18 and 24 months and expressive and receptive language at 24 months. Parent outcome measures include responsive parenting, family functioning, and parent engagement in the technology- supported platform. We will address the following research aims: Aim 1. document the feasibility and effects of the Social Communication Growth Charts and the Baby Navigator Class bundled on child and parent outcomes at 18 and 24 months; Aim 2. compare the effects of optimization with or without Mobile Coaching for slow responders on child and parent outcomes at 24 months; Aim 3. explore individual child and family characteristics that may moderate response to the technology-supported intervention components; and Aim 4. examine responsive parenting and parent engagement with each technology-supported intervention component and prepare for a full-scale SMART that will control for maturation. This study will enhance the sustainability, scalability, and lead to transformative changes to efficiently and effectively improve healthcare delivery via the use of innovative technology, an implementation science methodology, and user-friendly tools and web platform.